Poly(ethylene terephthalate) (PET) fibers are the primary type of polyester fibers produced by the textile industry. PET is synthesized by condensation, drawn into fibers from a melt, and can be cut into staple, or spun into yarn. The polyester can be dyed and knitted into cloth or made into carpets, or the polyester can be woven into fabric and dyed. The polyester can also be blended with natural fibers or other types of synthetic fibers to form polyester blends for use in these applications.
A common problem in the polyester industry is the formation of oligomer deposits during the production of polyester and various polyester textile products. These oligomers are formed as a by-product in the synthesis of polyethylene terephthalate and become deposited both on and in the polyester fibers. In particular, the amount of these oligomers in the polyester material can be up to 5% by weight. The presence of these oligomers on or in the polyester fibers can result in an undesirable grayish appearance of the final fabric. Furthermore, when the polyester is dyed, particularly with the disperse dyestuffs generally used for the dyeing of polyester fibers, fair non-dyed spots may remain on the dyed goods because of these oligomers. Moreover, the spinning of dyed polyester fibers that contain oligomers results in the formation of considerable amounts of dust, which causes further production problems. Additionally, oligomer deposits may impair the physical properties of the textile material such as for example the running properties and the feel of the textile material.
In addition to forming on and in the fibers, these oligomers can also become deposited on machinery. Specifically, oligomer deposits are transported throughout the production equipment and have a tendency to deposit on the stainless steel equipment in which the dyeings are conducted. As a result, the equipment requires frequent scouring under highly alkaline conditions to remove the material from the surface. In addition, solvents such as trichlorobenzene may also have to be incorporated into the cleaning solution. These processes require high temperatures and long treatment times, and are complicated to carry out. Very often, oligomer deposits are also found in the liquor pumps of the dyeing machines resulting in interruptions in production.
Those skilled in the art have therefore tried to remove oligomers from polyester by means of various after-treatment methods. For example, it is known that oligomers may partly be eliminated by rinsing the polyester with hot water or by subjecting the polyester to an alkaline reductive after-treatment in the presence of a tenside, for example a fatty acid polyglycol ester, at elevated temperatures. However, cyclic oligomers may be difficult to remove and resistant to such an alkaline post treatment. Therefore, to be effective, alkaline treatment must be severe, which results in a significant loss of polyester fiber material. Organic solvents have also been used to try to remove oligomers from polyester but it is difficult to find one that is compatible with and noninjurious to the textile material. Chlorinated hydrocarbons, fluorinated hydrocarbons and hydrocarbons themselves have also been used in the art to remove oligomer deposits.
All of the before-mentioned treatments used in the art pose production problems along with time and cost issues. Accordingly, there is a need in the art for removing oligomer deposits that results in minimal interruptions in production and poses little threat to the quality of the polyester or polyester textile product.